1. Field of the Invention
This invention relates to energy absorbers as extruded shapes made of aluminum alloy which have a high strength to resist a car body""s collision against a pole (aluminum is hereinafter called Al). It is also concerned with bumper stays to be attached to the body side face of the curved end portions of a bumper reinforcement having curved portions at both ends.
2. Description of Related Art
A car body incorporates body energy absorbers such as bumper reinforcements and door beams. The bumper fitted to the front or rear of the body has, in its inside, a bumper reinforcing member called a bumper reinforcement or bumper reinforce.
Recently, for the sake of lightness, there has been an increasing tendency to use extruded shapes of high-strength aluminum alloys (which have the same sectional profile in the longitudinal direction) such as JIS 5000, 6000 and 7000 series instead of steel shapes which were often used formerly.
Al alloys are higher in such energy absorption as mentioned above than steel if they have the same weight. As an Al alloy extruded shape which has the same sectional profile in the longitudinal direction, it is possible to efficiently mass-produce a rigid hollow structure whose sectional profile is virtually rectangular. For this reason, Al alloys are widely used for bumper reinforcements, bumper stays, door beams and so on.
However, a body energy absorber which consists of an Al alloy extruded hollow shape with a virtually rectangular sectional profile has the following problem: if it is used for rear bumper reinforcement, its bending strength may be insufficient with respect to the virtually horizontal force (of vehicle collision) applied to the body energy absorber when the body collides against a pole.
In order to prevent the body from being bent upon collision against a pole as mentioned above, the bending strength of the bumper reinforcement must be increased. There are various ways to increase it: increasing the strength of Al alloy itself as the material for the bumper reinforcement; increasing the thickness of web, front wall and/or rear wall; increasing the width of the bumper reinforcement and so on.
However, if the strength of the Al alloy shape is increased, it might be more difficult to make shapes by extrusion or bending and such shapes might be more likely to crack, resulting in less collision energy absorption. Also, an increase in the thickness of the Al alloy shape or the width of the bumper reinforcement will lead to an increase in weight, which means that the lightness of Al alloy is traded off for increased strength. If the thickness of the Al alloy shape should be simply increased, the maximum load (force) of a collapsing bumper reinforcement might be larger than the permissible maximum load for side members, and it would be very likely to damage body members such as front side members.
J-P-A-No. 286536/1994 discloses a reinforcement structure in which an auxiliary hollow shape reinforcement made of Al alloy (which has, for example, a semicircular sectional profile at the front and a planar one at the rear and incorporates two props or ribs) is glued to the longitudinal center of the bumper reinforcement front side.
If an auxiliary steel reinforcement as mentioned above is used, the auxiliary reinforcement weight to obtain a satisfactory reinforcing effect is added, which offsets the advantage of lightness offered by the use of Al alloy for an energy absorber.
The auxiliary reinforcement in the form of a hollow shape of Al alloy as described in the above-said J-P-A-No. 286536/1994 may be lighter than the above-said steel reinforcement. Yet still, because the weight of the hollow shape reinforcement with a closed sectional profile is added, the problem of weight increase remains in comparison with the case of absence of an auxiliary reinforcement.
According to the above-said gazette, it is possible to lighten the bumper reinforcement main body as an Al alloy hollow shape by using an auxiliary reinforcement and decreasing its wall thickness. However, the auxiliary reinforcement has a hollow structure with a closed sectional profile and uses inner ribs (props) to reinforce it, so the collapse strength of the auxiliary reinforcement is rather high. Therefore, if the wall thickness of the bumper reinforcement main body is decreased as stated above, upon collision against a pole or in a similar situation, the bumper reinforcement main body might collapse earlier than the auxiliary reinforcement.
Further, because the auxiliary reinforcement is a hollow shape with a closed sectional profile, it is virtually impossible to join it to the bumper reinforcement main body mechanically or using bolts or the like or by welding. Consequently, the fixing method which uses glue as described in the gazette is unavoidable. However, gluing is much more unreliable as a method for fixing a vehicle structural member than a mechanical fixing method or welding.
It is thus demanded that a car body energy absorber such as a rear bumper reinforcement should have a sufficient bending strength without its lightness being unfavorably affected and without a decline in energy absorption upon body collision against a pole, and never bend horizontally from its center or cause buckling upon such collision.
Usually, the bumper reinforcement is fixed to the car body through car body couplers such as bumper stays. In case of a bumper reinforcement which has a curved (or curved) portion at each end, the surface of the bumper stay to come into contact with the bumper reinforcement must match the curved surface of the latter in attaching the former to the latter. Even when the contact surfaces of both are matched, there still remains another problem: how they should be joined and fixed. One known approach as the prior art is that bolts are passed through both the hollow of the curved portion of the bumper reinforcement and that of the bumper stay to connect them with the top and bottom of the bolts staying in these hollows. A conventional technique for joining and fixing a bumper stay to a side member on the bumper stay""s car body side is that a hollow attachment as an integral part of the bumper stay is provided and the stay is joined and fixed to the side member through the attachment. This attachment has a width that matches the width of the side member.
Then this hollow attachment is placed in position on the side member and engaged with it. Bolts are passed through this engagement horizontally from the side of the car body and the stay and side member are fixed with the top or bottom of the bolts staying in the hollow of the side member or attachment.
However, these conventional joining/fixing methods have drawbacks. First of all, they are impractical and sometimes even ineffective.
In the above-said conventional methods, it is practically difficult to put a bolt into the inside of the bumper reinforcement and stay which are both hollow and have a closed sectional profile. It is even more difficult for a bumper reinforcement with a curved portion at each end. It is also practically difficult to let the bolt""s top and bottom stay in the hollows with the bolt passed through them as suggested by the conventional methods.
Further, it is unrealistic to join and fix the stay to the front of the side member according to the prior art for the following reasons. One reason is that it is difficult to position the above-said hollow attachment on the side member in the car body widthwise direction.
Besides, even if the hollow attachment is once positioned on and engaged with the side member, it is difficult to let the bolt""s top or bottom stay in the hollow of the side member or stay attachment with the bolt passed through them horizontally from the side of the car body.
A first object of this invention is to provide a car body energy absorber as a strengthened version of Al alloy car body energy absorber which does not damage the car body as it bends upon car body collision against a pole, where the lightness and high energy absorption performance are maintained.
According to this invention, a car body energy absorber which achieves this object consists of a hollow shape with a rectangular sectional profile and a reinforcing shape to be attached to the front face of the collision plane of the hollow shape. The reinforcing shape consists of the following: a collision wall which is almost parallel to the collision plane of the hollow shape; plural horizontal ribs attached to the collision wall which are parallel to each other; and vertical flanges protruding outward from the reinforcing shape, located at the tips of the horizontal ribs, opposite to the collision wall. The reinforcing shape is connected with the collision plane of the hollow shape through the vertical flanges.
The car body energy absorber according to this invention offers the following advantages. Firstly, since the hollow shape and the reinforcing shape are aluminum alloy extruded shapes, the overall weight of the absorber is smaller and the weight increase due to the addition of the reinforcing shape is also relatively small. Secondly, what is particularly important is that, since the reinforcing shape has not a hollow, closed rectangular sectional profile having four sides but an open sectional profile and, it is possible to increase the strength while maintaining the weight increase due to the addition of the reinforcing shape at the minimum level. Thirdly, it is easy to attach because the reinforcing shape is connected with the hollow shape""s collision plane through the vertical flanges located at the tips of the horizontal ribs.
Furthermore, in the car body energy absorber according to this invention, the hollow shape may be larger (in height and width) than the conventional type of absorber with a rectangular sectional profile because it is reinforced by a center rib.
In addition, in the car body energy absorber according to this invention, the horizontal ribs and the vertical flanges are connected in a manner that their intersections each form a circular arc, or so that the horizontal ribs of the reinforcing shape bend inwards in the cross section of the shape when a force is applied almost horizontally. Thanks to this, the decrease in resistance to the applied force which may be caused by deformation, is smaller and the collision energy is more absorbed than when the horizontal ribs of the reinforcing shape bend outwards in the cross section.
Consequently, in case of a less significant collision with a relatively small force applied almost horizontally, it is likely that the hollow shape does not collapse and only the reinforcing shape collapses. This offers the advantage that only the reinforcing shape need be replaced in repair after the collision.
The car body energy absorber according to this invention uses one of AA or JIS 5000, 6000 and 7000 series of Al alloys. Since these Al alloys are excellent in formability and have a high strength, they are easily manufactured by extrusion and other techniques and can provide a higher collision energy absorbing power.
Because of these excellent characteristics, the car body energy absorber according to this invention is particularly suitable for use as a reinforcement for the vehicle rear bumper or front bumper.
A second object of this invention is to provide a stay as an Al alloy extruded shape which is easily attachable to the rear face of the curved portion of the bumper reinforcement end and the front face of the side member as well as a bumper reinforcement integrated with stays which is easily attachable to the side member.
In order to achieve this object, this invention provides a bumper stay to be attached to the car body side surface of each end portion of the bumper reinforcement, where the bumper stay consists of the following: a front wall whose shape matches the car body side surface of each end of said bumper reinforcement; at least two side walls which support said front wall from the car body side; and a rear wall connected with the side wall end opposite to said front wall. The rear wall and the side walls meet virtually at right angles. The front wall has flanges protruding outward from the bumper stay.
In a stay according to this invention, particularly when each end of the bumper reinforcement has a curved portion which is bent toward the rear of the car body, the front wall of the stay is shaped in a way to match the shape of the rear face of each end of the bumper reinforcement or so that it has an inclination to match the rear face of the curved portion. In addition, the stay is characterized in that its front wall has flanges protruding at both ends of the stay (or side walls).
Therefore, in comparison with the above-said conventional stay whose front wall has no flanges, this stay is easily attached because these flanges enable and facilitate mechanical connection with the rear face of each curved end of the bumper reinforcement by means of bolts and nuts or rivets. In other words, the introduction of these flanges makes it easy to join and fix the stay to the above-said car body side surface of each end of the bumper reinforcement, and also to the front face of the side member at its rear wall.
If an electrode can be put in the hollow of the above-said curved end of the bumper reinforcement or the like, the electrode can be easily attached to the flanges so it is possible and easy to use spot welding. It is also possible and easy to connect the stay with the bumper reinforcement by welding on the flange end and along the rear face of the curved portion to be in contact with this end. A combination of these connecting methods can be used, which means that various options with regard to the connecting method are available. This is one of the major advantages of the stay according to this invention.
In this respect, the flanges can be easily and mechanically joined and fixed to the rear face of each curved end of the bumper reinforcement, for example, by means of self-piercing rivets, bolts or something like that.
Also, by making holes in the flanges, the bumper stay can be easily and mechanically joined and fixed to the rear face of each curved end of the bumper reinforcement through these holes by means of bolts or something like that.
Also, the bumper stay can be joined and fixed to the rear face of each curved end of the bumper reinforcement by welding on the flanges.
The stay according to this invention has holes in its rear wall. Therefore, it can be easily joined and fixed to the front face of the side member through these holes by means of bolts or something like that.
Further, the stay according to this invention has working holes in the front wall excluding the flange areas. Therefore, even if the stay has a hollow structure with a closed sectional profile, the rear wall of the stay can be easily joined and fixed to the front face of the side member through these holes by means of bolts or something like that.
Further, the stay according to this invention has an open sectional profile with working holes in the front wall excluding the flange areas. Therefore, even if the stay has a hollow structure with a closed sectional profile, the rear wall of the stay can be easily joined and fixed to the front face of the side member through these holes by means of bolts or something like that.
The stay according this invention has a hollow sectional profile which is composed of a front wall, side walls and a rear wall as mentioned above, resulting in improvement in the collapse strength of the stay.
However, if the stay has a hollow, closed sectional profile, it would be difficult to attach it to the side member. To facilitate its connection with the side member, it is desirable to have an attachment for connection with the side member at the rear side of the rear wall.
The stay according to this invention is made of an Al alloy which is chosen from among AA or JIS 5000, 6000 and 7000 series Al alloys. These Al alloys are suitable for the stay according to this invention because they are excellent in formability, have a high strength and can thus be easily manufactured by extrusion or a similar technique.
In addition, the stay according to this invention may be pre-assembled on the bumper reinforcement to make up a bumper reinforcement integrated with stays. To install a conventional stay, the car manufacturer must take two steps: (1) attachment of the stays to the side members and (2) attachment of the stays to the bumper reinforcement. Contrary to this, the bumper reinforcement integrated with stays according to this invention only requires the car manufacturer to take step (1) or attachment of the stays to the side members, because the bumper reinforcement is pre-assembled with the stays.
Furthermore, it is most desirable to make up a bumper by combining the above-said bumper reinforcement as a car body energy absorber which achieves the first object of this invention and the above-said bumper stays which achieve the second object of the invention.